1. Technical Field of the Invention
The present invention relates generally to a fuel injection system such as a common rail system (also called an accumulator fuel injection system) for automotive diesel engines which is designed to spray jets of high-pressure fuel supplied from an accumulator into cylinders of the engine through fuel injectors, and more particularly, to such a system designed to monitor an abnormal pressure of fuel sucked into a fuel pump for supplying the fuel to the accumulator.
2. Background Art
There are known accumulator fuel injection systems which are equipped with a common rail in which fuel is accumulated at a target pressure, as determined as a function of an operating condition of an internal combustion diesel engine, injectors working spray the fuel accumulated in the common rail into the engine, a fuel supply pump driven by output power of the engine to supply the fuel to the common rail, and a controller working to control operations of the injectors and the fuel supply pump.
There are also known accumulator fuel injection systems equipped with a low-pressure supply pump and a high-pressure supply pump. The low-pressure supply pump is installed in a fuel tank and driven by a power source other than the engine such as an electric motor to pump the fuel from the fuel tank. The pumped fuel is regulated in pressure by a pressure regulator and then sucked into the high-pressure supply pump.
In recent years, there has been an increasing need for the later type of fuel injection systems to detect an abnormal pressure of fuel at an inlet of the high-pressure supply pump in a simple manner in terms of improvement of the performance and durability thereof. For example, use of a pressure sensor has been proposed which is installed in a fuel flow path leading to an inlet of the high-pressure supply pump to measure the pressure of fuel sucked into the high-pressure supply pump directly.
The use of the pressure sensor, however, results in an increase in total production cost of the systems and a need for creasing a space for installation of the sensor.
For instance, Japanese Patent First Publication No. 8-158971 (U.S. Pat. No. 5,626,114) teaches techniques for regulating the pressure of fuel at an outlet of the high-pressure supply pump without use of an additional relief valve. Such techniques are suitable for regulating the pressure at the outlet of the high-pressure supply pump, but have a difficulty in regulating the pressure at the inlet of the high-pressure supply pump.